8 VARIATION UNDER DOMESTICATION. [CHAP. I. 



pagated by grafts, offsets, etc., and sometimes by seed. They occur 

 rarely under nature, but are far from rare under culture. As a 

 single bud out of the many thousands, produced year after year on 

 the same tree under uniform conditions, has been known suddenly 

 to assume a new character ; and as buds on distinct trees, growing 

 under different conditions, have sometimes yielded nearly the same 

 variety for instance, buds on peach-trees producing nectarines, 

 and buds on common roses producing moss-roses we clearly see 

 that the nature of the condition is of subordinate importance in 

 comparison with the nature of the organism in determining each 

 particular form of variation ; perhaps of not more importance 

 than the nature of the spark, by which a mass of combustible 

 matter is ignited, has in determining the nature of the flames. 



Effects of Habit and of the Use or Disuse of Parts ; Correlated 

 Variation ; Inheritance. 



Changed habits produce an inherited effect, as in the period of 

 the flowering of plants when transported from one climate to 

 another. With animals the increased use or disuse of parts has 

 had a more marked influence ; thus I find in the domestic duck 

 that the bones of the wing weigh less and the bones of the leg 

 more, in proportion to the whole skeleton, than do the same bones 

 in the wild duck ; and this change may be safely attributed to the 

 domestic duck flying much less, and walking more, than its wild 

 parents. The great and inherited development of the udders in 

 cows and goats in countries where they are habitually milked, in 

 comparison with these organs in other countries, is probably 

 another instance of the effects of use. Not one of our domestic 

 animals can be named which has not in some country drooping 

 ears ; and the view which has been suggested that the drooping 

 is due to disuse of the muscles of the ear, from the animals being 

 seldom much alarmed, seems probable. 



Many laws regulate variation, some few of which can be dimly 

 seen, and will hereafter be briefly discussed. I will here only allude 

 to what may be called correlated variation. Important changes in 

 the embryo or larva will probably entail changes in the mature 

 animal. In monstrosities, the correlations between quite distinct 

 parts are very curious ; and many instances are given in Isidore 

 Geoffroy St. Hilaire's great work on this subject. Breeders believe 

 that long limbs are almost always accompanied by an elongated 

 head. Some instances of correlation are quite whimsical : thus cats 

 which are entirely white and have blue eyes are generally deaf ; but 

 it has been lately stated by Mr. Tait that this is confined to the 

 males. Colour and constitutional peculiarities go together, of which 

 many remarkable cases could be given amongst animals and plants. 



